This dissertation concerns the development of market information technologies in the London Stock Exchange, c. 1945-1992. Based on archival research in London, Cambridge and Edinburgh, and 20 semistructured interviews with former technologists, brokers, and marketmakers, my dissertation identifies the social, technological and institutional factors that allowed dealings in bonds and equities to move off the trading floor of the Stock Exchange and onto competing electronic platforms. My dissertation utilises the history of market information technologies as an occasion for producing a multi-layered analysis of the material, social, and regulatory transformations of finance in the City of London between c. 1945 and the mid 1990s. In particular, my dissertation deals with the rise of the so-called ‘information age’ in relation to British finance. The analysis is carried out in three parts, each tackling a specific ‘myth’ on the role of information and communication technologies in contemporary finance. The first part (chapters 3-4) deals with the dematerialisation of finance, demonstrating the often ignored character of technologies, materialities and their associated expertise in the constitution of the market. The second part (chapter 5) deconstructs the concept of disintermediation by analysing the social history of broking and jobbing in post-war City of London. Specifically, this part argues that changes in financial practices amongst the membership of the Stock Exchange were neither determined by the adoption of computers nor defined by a pre-existing culture of gentlemanly capitalism. Rather, they derived from the adaptation of market participants to a changing economic and social environment. The third part of this thesis (chapter 6) engages with deregulation. In particular, it provides an account of three broad patterns of financial regulation in Britain and the emergence of the current understanding of financial markets as manageable entities. The dissertation finalises by exploring the role of ‘informational metaphors’ in mediating the practices, materialities and regulations of the London Stock Exchange.